The present invention is directed at lube oil manufacture. More specifically, the present invention is directed at increased production of deasphalted oil.
As process improvements have been made in the production of lube oil, frequently deasphalting becomes the production limiting operation. Declines in the quality of the crudes utilized for lube oil manufacture often necessitate higher throughputs to obtain a predetermined amount of product. In addition, elevating the coil outlet temperature in vacuum pipestills to increase the production of distillates will decrease the amount and increase the viscosity of the residuum which is passed to the deasphalting zone. This in turn, limits the amount of acceptable quality deasphalted oil that can be produced. Thus, to maintain production of a fixed amount of deasphalted oil, additional amounts of residuum ordinarily must be passed through the deasphalting zone.
However, where the deasphalting zone is operating at or near its design capacity, it may not be desirable or possible to increase the feed rate to the deasphalting zone. Increasing the feed rate may result in inadequate deasphalting of the residuum. Increasing the deasphalting zone capacity often may not be feasible, due to space limitations or may not be economical due to the associated capital and operating costs for the additional deasphalting zone and solvent recovery facilities.
It has been known to improve the quality of the residuum passed to the distillation zone by adding distillate from the vacuum distillation zone to the vacuum residuum. U.S. Pat. Nos. 3,929,626 and 3,989,616 disclose admixing overflash from the distillation zone with residuum from a vacuum distillation prior to deasphalting. This process is reported to increase the quantity of blending stocks recovered. However, this process may decrease the quality and quantity of distillates produced. Since the overflash is a distillate, removal of this stream will decrease the total distillate production. Moreover, since the overflash also serves as an internal wash in the vacuum pipestill to improve the separation of distillate from the residuum, decreasing the quantity of this stream may adversely affect the distillate product quality.
It is desirable to provide a process in which the overall production of deasphalted oil is increased without adversely affecting the quality or quantity of distillates produced from the crude.
It also is desirable to increase the production of deasphalted oil without an expansion of the deasphalting and/or solvent recovery operations.
It also is desirable to produce a deasphalted oil having low Conradson Carbon Residue and low metals content, so that valuable end products, such as lube blending stocks and/or fuels products, can be produced by further processing.
The present invention is directed at passing residuum from a first distillation zone through a second distillation zone. Distillate from the second distillation zone is admixed with additional residuum. The mixture subsequently is deasphalted to produce a deasphalted oil.